Various methods are used to seal between tubular goods and casings in wells, specifically water wells. The seal is necessary, for instance, to seal off between the upper end of a perforated screen located in the production zone and the casing. This seal prevents contaminated water from coming around the screen and entering the casing to be pumped to the surface. If the well is not too deep, and the casing is not cemented in, the screen can be attached directly to the lower end of the casing and no seal is required.
If, on the other hand, the casing is cemented in, and the screen cannot be attached directly to the casing, it is necessary to lower the screen into the casing and then flush out contamination such as drilling fluids. Flush water returns to the surface by way of an annular space between the screen and the casing. Flushing is done by running a wash pipe down into the interior of the screen and by running wash water through the wash pipe through a back pressure valve and out a plug at the end of the screen, thereby flushing all contamination back up past the upper end of the screen through the casing to the surface.
After this flushing has taken place it is necessary to seal between the upper end of the screen and the inside surface of the casing to prevent any water from being pumped to the surface without going through the screen. This seal can be accomplished in various ways. The most common seal is called a lead seal. It is composed of a deformable lead skirt which is threaded onto the upper end of the screen. This lead seal is lowered into the casing, along with the screen, on the end of a drill pipe. After flushing has taken place as described before, the drill pipe is removed and a sealing iron is run into the casing to permanently seal the lead seal against the casing. The problems associated with using a lead seal are that lead should not be used in constant direct contact with drinking water where avoidable, that the lead seal sometimes seals imperfectly allowing some leakage, and that the installation of the lead seal sometimes damages the casing or the sealing surface itself.
Another known method of sealing a well uses a deformable rubber seal having a screen insert which is sealed against the casing at the appropriate time by insertion of a tool to flare the seal out against the casing, much like the process used with lead seals. This method still requires that the drill pipe be removed from the screen and pulled from the casing and a flaring tool attached to the drill pipe which is then reinserted into the well in order to perform the sealing operation. As with a lead seal, this pulling and reinsertion of the drill pipe can consume several hours, resulting in increased costs. In addition, the deformable seal has no positive means of insuring that contact with the casing is always maintained.
It would be beneficial to avoid the use of lead in any such seal and it would also be beneficial to accomplish the sealing operation without removal of the drill pipe from the casing, attachment of a sealing tool and reinsertion of the drill pipe. Finally, it would be beneficial to have some means that would insure that the seal remains in constant contact with the inner surface of the casing.